The Collaborative International Dictionary of English v.0.48:

arbitrager \arbitrager\ n.
   same as arbitrageur.

   Syn: arb, arbitrageur
        [PJC]

WordNet (r) 3.0 (2006):

arbitrager
    n 1: someone who engages in arbitrage (who purchases securities
         in one market for immediate resale in another in the hope
         of profiting from the price differential) [syn:
         arbitrageur, arbitrager, arb]